1. Field of the Invention
The present invention relates to an unlocking system for use with cards, and more particularly to such an unlocking system useful for buildings, such as hotels, having large numbers of rooms which must be locked and which are unlocked frequently by different persons.
2. Description of the Prior Art
Hotels have large numbers of rooms which must be locked. Each of such rooms is usually provided on the door with a mechanical lock, such as a tumbler lock, which is opened and closed with a key. In the case of locks for use with keys, the hotel clerk must hand the key to a guest when he checks in and must receive the key when he checks out. Thus the maintenance of keys is very cumbersome. Further when a key is lost, there arises the necessity of replacing the lock itself to assure security. This requires time and cost.
Accordingly an automatic unlocking system has been proposed which opens a lock in response to an electric signal and which comprises as mounted on a door a card reader, a memory for storing a secret number and a processing unit. A card having a secret number magnetically recorded thereon is used for this system. With this system, the secret number read from the card by the card reader is compared with a secret number stored in the memory, and when a match is found between the two numbers, the lock is opened. Every time a different guest is assigned the same room, a card having a new secret number recorded thereon is handed to the guest. The secret number is changed by a central control unit for concentrically controlling a large number of rooms. Every time the secret number is changed to a new one, the changed new number is transmitted from the central control unit to the memory of the room concerned. Accordingly this system needs a communication cable between the central control unit and the unlocking unit of each room. Such cables are costly to install and require maintenance and inspection periodically.
Another unlocking system is known which does not require the installation of communication cables between the central control unit and the unlocking units at rooms. With this system, a newly issued card bears a new secret number in addition to the old secret number. An unlocking unit installed on the door compares the new secret number on the card with a secret number stored in a memory to check whether or not the two numbers are identical. If the numbers are not identical, the unit subsequently checks whether the old secret number on the card matches the secret number in the memory. If they are found to match, the lock is opened, and the new secret number on the card is stored in the memory. Although random numbers are used as the two secret numbers on the card, the card is simple and easy to counterfeit because the card bears only two numbers. The system therefore involves a security problem.
With either one of the systems described above, the secret number is changed when the room is assigned to a different person, so that if the room is not used subsequently for some other guest, the secret number stored in the memory remains the same as the number on the card for the previous guest. With hotels, the same room frequently remains vacant for several days. In such a case, it becomes possible for the previous guest to use the room without paying the charge until the next guest registers for that room.